The present invention relates to a method and apparatus for electrically stimulating muscle and, more particularly, to a computer controlled method and apparatus for monitoring muscular activity and adjusting an electrical stimulus to provide controlled and sustained isokinetic contractions. Still more particularly the present invention relates to a method and apparatus for directing coordinated movement of several muscles and exercising them through a specific exercise routine having therapeutic applications in the treatment of paralysis.
The invention which is disclosed and claimed herein has particular value in the treatment of persons who have suffered injuries resulting in spinal cord damage. This particular type of damage often times produces partial or total paralysis of muscles which are controlled from a point below the point of spinal cord damage. The victim then faces a life of relative inactivity and deterioration of muscles which otherwise would be active. It has now been found in accordance with this invention that such muscles can be stimulated to engage in an exercise program once thought to be impossible. Moreover, it has been found that such an exercise program can restore normal muscle tone, even after years of inactivity.
Since the work of Galvani in 1791, it has been known that electricity can be used to induce muscle contractions. Recently, there has been increased awareness of the value of electrostimulation in muscle therapy.
Numerous devices and techniques have been developed for supplying electrical pulses as part of a therapeutic regime of muscle stimulation. Several examples of these are found in the patent literature. Radwan, U.S. Pat. No. 3,387,147 (1968) discloses a muscle stimulating pulse generator designed to provide a pulse signal having a relatively high voltge-to-width ratio and a steep rising wavefront.
Maurer, U.S. Pat. No. 3,817,254 (1974), discloses a transcutaneous stimulator for use in suppressing pain designed to differentially stimulate touch versus pain nerve fibers in an effort to reduce the prickly sensation known to accompany some pain therapy. Maurer notes that differences in the response of nerves to electrostimulation can be used to selectively stimulate different types of nerves. According to Maurer, nerve fibers are distinguished in terms of their size and conduction velocity. He notes that the amplitude of electrical stimulation required to elicit a muscle response increases as the fiber size decreases.
Nawracaj et al, U.S. Pat. No. 4,071,033 (1978), discloses an electrostimulation device which utilizes a heterodyne effect to produce an otherwise painful low frequency stimulus in a muscle and cause the muscle to contract and relax at a low frequency.
Wyss et al, U.S. Pat. No. 4,148,321 (1979), discloses a muscular therapy similar in some respects to Nawracaj et al wherein muscles are made to rhythmically contract and relax at a very low frequency which is induced by modulating a medium frequency current between 3,000 and 100,000 Hz with a low frequency current less than 1 Hz. In one embodiment Wyss et al uses a phase shifter to transform the modulated output current into a three phase current, which is delivered to three electrodes angularly spaced about a limb to provide deep uniform stimulation.
Kofskey et al, U.S. Pat. No. 4,177,819 (1979), teaches an apparatus for stimulating a muscle for 2 to 20 seconds at 2 to 50 second intervals using a 2000 to 3000 Hz signal modulated at 40 to 50 Hz. In one embodiment, the muscle stimulating waveform is controlled by a microprocessor which gradually increases and decreases the amplitude of the stimulation at the beginning and end of each pulse. The microprocessor responds to signals from a no-load/overload sensor and to a manually controlled gain setting signal.
It can be seen that the efforts embodied in the foregoing patents focus on the stimulus itself as the therapeutic agent and have as a principal objective to optimize the intensity, duration and frequency of the stimulus to enhance its therapeutic effects. In the disclosed therapies, the muscle is not stimulated against a load. These prior art systems do not provide smooth isometric contractions and do not respond to muscle activity response to muscle activity in these prior systems.
In order to train a muscle and make it physically strong, it is necessary to work the muscle against a load while producing powerful, sustained, isokinetic contractions at a substantial proportion of the muscle's strength. Isokinetic contractions cannot be maintained for prolonged periods of time in the aforementioned therapies, because they stimulate the muscle synchronously using frequencies much higher than normal physiological frequencies. This causes the muscle to fatigue rapidly, making it impossible to maintain muscle tension.
It has been found that considerable insight regarding the response of human muscles to electric stimulation may be gained by experimentation with cats. The present inventors began their work by such a program, and the results thereof are described in the technical literature. See for instance Petrofsky and Phillips "Microprocessor Controlled Stimulation in Paralyzed Muscle", IEEE NAECON Record (1979), 198-210 and other articles cited therein, all of which are herein incorporated by reference.